1. Field of the Invention
This invention pertains to balloon catheter angioplasty and more specifically to dilation of an obstructed vessel in the human anatomy by a balloon catheter of novel design for use in the treatment of arterial occlusive disease.
2. Description of the Prior Art
At the present time, the technique to perform angioplasty has employed a basic pattern. Once it has been determined that angioplasty is to be employed to treat an arterial occlusion, a guiding catheter is used to lead a balloon catheter to the aortic origin of the vessel to be dilated, while also allowing monitoring of aortic pressure. In addition, the guiding catheter permits dye injections to clarify the vascular anatomy during the procedure in a manner similar to that employed when a smaller diagnostic vascular catheter is employed for diagnostic angioplasty. Once the lesion is reached, the guiding catheter supports the balloon catheter as it crosses the lesion addressed.
The balloon catheter system comprises the balloon catheter and a guidewire. The essential function of the balloon catheter system is to carry safely an inflatable balloon across a vascular obstruction. The guidewire used in the system must be visible on fluoroscopy, it must be delicate and the proximal end thereof must be responsive when manipulated from outside. Historically, these requirements have led to the development of the so-called "removable, steerable" guidewire concept. Typically, a 0.014" to 0.018" guidewire is passed through the balloon catheter and manipulated independently. This system, therefore, allows for the removal of the guidewire, while leaving the balloon catheter in the vascular position attained and permits the use of different guidewires having various qualities and tip shapes.
Prior art balloon catheters have these two essential features: (1) they are capable of carrying the balloon to the desired position through the occluded vascular segment, and (2) they allow the inflation and deflation of the balloon from an external port. Most of the balloon catheters have a double passageway or lumen: (1) a first one dedicated to inflate and deflate the balloon with a hydraulic system and (2) a second one for passing the guidewire therethrough while being large enough to maintain a channel around it to permit monitoring of the tip pressure (i.e., the inside pressure of the vascular system) or alternately to permit monitoring of the vascular anatomy by radiographic dye injection.
It has become apparent during the last few years of clinical experience that attaining the lowest profile of the balloon catheter system is quite desirable in order to facilitate the passage of the balloon across severe and remote vascular obstructions. This technological challenge has led to two simplifications of the above-described balloon catheter system. A first simplification referred to as the "Hartzler's design" sacrifices one lumen of the balloon catheter. This leads to the need for a non-removable and/or non-independently steerable guidewire (i.e., the whole system of wire and balloon catheter steers). In such a design the capacities for monitoring pressure and for dye injection to determine vascular anatomy are consequently lost. In a second simplification, the guidewire is made hollow and carries an inflatable balloon on its tip. This structure is sometimes referred to as the "balloon-on-the-wire" system. In this system, the capacities of monitoring distal pressure and anatomy by dye injection are also lost, while the steerability remains impaired as it is necessary to steer the balloon with the system. It must be noted here that guidewires that are not attached to a balloon catheter distally can be advanced and/or rotated with precision. By contrast, when the balloon catheter is attached distally to the guidewire the bulkiness of the balloon impairs the precise advancement or rotation of the guidewire, while the balloon itself may become twisted by steering the system.
The structure disclosed herein achieves a low profile in the balloon catheter system by reducing catheter wall thickness, while maintaining at least most of the favorable qualities of the traditional so-called "steerable, removable guidewire system". In double lumen balloon catheters, as described above, typically four walls are present in a cross-sectional diameter. Each of these walls when made of such conventional materials as polyethylene, polyurethene and polyvinyl chloride has a thickness of at least 0.005 inch. This fact leads to having at least 0.020 inch in the cross sectional diameter of such traditional double lumen catheters dedicated to material only. This material cross-sectional space constitutes a sizable portion of the entire cross sectional thickness, which typically is 4.3 French or 0.0056 inch. A minimum of 0.005 inch wall thickness is required when these materials are used in order to withstand inflation pressures and to prevent collapsing of the catheter body walls when vacuum is created to deflate the balloon.
A different and newer material is employed in the inventive structure herein set forth to build a double lumen catheter. The material is polyimide plastic, which has a tensile strength 3-5 times greater than conventional materials. Use of such materials results in significant economies in the cross sectional diameter dimension of the balloon catheter. Only a total of 0.004 inch of cross sectional diameter of an otherwise typical double-lumen balloon catheter is occupied by the catheter walls. Having realized a significant saving in material thickness, the new balloon catheter described hereinafter not only will have a low profile at the level of the balloon, which therefore becomes the critical profile in terms of capacity of crossing severe vascular obstructions, but also will enable the usage of traditional diagnostic catheters to guide the balloon catheter system. This is an advantage as traditional diagnostic catheters have excellent torque control and distal tip flexibility and curve memory compared with guiding catheters commonly used in angioplasty. In addition, diagnostic catheters seat better than the guiding catheters commonly used in the ascending aorta and the use of a diagnostic catheter to guide the balloon catheter results in less of a chance for the balloon catheter to dislodge from the coronary orifice when the balloon catheter is advanced in the coronary arteries.
It must be recalled at this point that balloon catheter angioplasty is currently being done by using a guiding catheter, which is different from the catheters used for diagnostic angioplasty. Such guiding catheter has a non-thrombogentic and Teflon lined, low friction inner lumen of relatively large inner diameter (typically, 0.070-0.072 inch), which does not taper at the tip, thereby having poor distal tip flexibility, and which results in a less adequate torque control and curve memory than achieved by diagnostic catheters.
As set forth more fully hereinafter, the embodiments of polyimide plastic catheters, being lower in cross section, angioplasty (e.g., having a dimension of 6 or 7 French) as a guiding catheter, thereby resulting in an economy of materials, time expenditure, and a reduction in patient risk during angioplasty.
Additionally, the new balloon catheter system described herein allows for an improved progressive maneuver for advancing the balloon catheter over the guidewire. The presently used systems find frequently difficulty in forcing the balloon tissue through the occlusive lesion, even after passing the guidewire. Most commonly, this passage is accomplished by simultaneously locking the guiding catheter into the arterial ostium or origin of the addressed vessel and pushing the balloon catheter slowly, while gradually retrieving the guidewire, which previously had already passed through the lesion.
In one embodiment of the present structure, a new mechanical device is disclosed that allows for a gradual, forced protrusion of the balloon tip over the guidewire. This device is sometimes referred to herein as a "mechanical slider". Such a mechanical slider device allows for enhanced pushing forces to be safely and gradually used by a single operator physician. Hence, using such device in combination with the catheter structure disclosed herein provides a maneuver that is both important from a safety point of view, as well as providing economies in physician time usage.